The thermo-chemical conversion by steam treatment of biomass material has been described earlier in a series of articles. One such article appears in the American Chemical Society Symposium Series 76 on Solid Wastes and Residues--Conversion By Advanced Thermal Processes, presented at a meeting of the American Chemical Society at Anaheim, Calif., USA on Mar. 13-17, 1978, in a paper entitled "Power From Wastes Via Steam Gasification" by John A. Coffman and R. H. Hooverman. This was a follow-on report of earlier work described in a paper entitled "Rotory Kiln Gasification of Biomass and Municipal Wastes" presented by John A. Coffman and R. H. Hooverman at a symposium on clean fuels from biomasses and wastes sponsored by the Institute of Gas Technology at Orlando, Fla., USA on Jan. 25-28, 1977. The work on steam gasification reported in these two papers led to a design for a fixed kiln with a rotor in which the steam gasification process is conducted, which was described in a paper presented at the 14th Biomass Thermal Chemical Conversion Contractors meeting held in Arlington, Va., USA on June 23-24, 1982 and published in the Proceedings of that meeting in October 1982.
While the fixed kiln with rotor described in the October 1982 Proceedings of the 14th biomass Chemical Conversion Contractors meeting possessed many desirable characteristics, it nevertheless was not entirely satisfactory due to a number of objectionable characteristics including tendency to compaction and agglomeration of certain biomass material sought to be gasified in the apparatus. In addition, difficulty was encountered in maintaining good thermal conductivity between hot feedback gases in feedback conduits employed to heat the biomass in the apparatus and the hot gas feedback conduits had a tendency to clog. Further, the complexity and cost of the rotor design made the apparatus expensive to manufacture. Additionally, certain types of biomass material required excessively long treatment time in order to obtain satisfactory gasification in a reasonable length apparatus. Lastly, difficulties were encountered in feeding vastly different types of input biomass material into the apparatus in a manner such that compaction and agglomeration both at the input and throughout the apparatus is prevented. To overcome these problems, the present invention was devised.